1. Field of the Invention
The present invention relates generally to electro-optic polarizors, and particularly to electro-optic polarizors for use in optical communications systems, such as a variable optical attenuator (VOA), a dynamic gain flattening device or other optical components.
2. Technical Background
As one optical component example out of others used in a network, a variable optical attenuator (VOA) is one of the basic building blocks of an optical communications system. The VOA is used to reduce the power level of an optical signal in a tunable manner. The input optical power is higher than the output optical power by a factor of 1/k in which k is the variable attenuation coefficient and is varied by VS the control signal. The output optical power is thus proportional to the input optical power reduced by a factor of k. The magnitude of k is controlled by VS and is limited to the range from 0 to 1.
Several methods presently exist for implementing a VOA. The two most actively pursued include: opto-mechanical methods such as a moving blade or a variable neutral density filter; and electro-optic methods such as using traditional passive liquid crystal technology. The traditional liquid crystal based VOAs offer a low voltage, low cost advantage over the opto-mechanical devices but typically suffer from temperature effects, polarization dependent loss, when the removal of polarization from the different orthogonal coordinates are not equal, or unacceptable insertion losses due to the existence of separate polarizers. A dual polarization path system can be used to overcome these prior-art polarization deficiencies. However, an added cost is incurred for the addition of polarization splitters and combiners.
Most liquid crystal devices use transverse electric fields. In the transverse field the electric field lines extend from the first substrate to the second substrate of the liquid crystal (LC) material sandwiched in between.
In such traditional LC devices that use transverse fields, the resolution is limited to approximately five times the film thickness due to electrical crosstalk from the fringing field of adjacent electrodes. Therefore, a trade-off exists between resolution and useful LC film thickness. High quality structures are thus not likely for features or grating periods below 10 xcexcm.
The alignment needed for the passively aligned transverse field LC device is homogeneous which is usually achieved by a complex rubbing process.
Therefore, there is a need for a simple, non-mechanical, low cost, low voltage, low power, high resolution, arrayable device or method to control polarization for use as an optical communication component, such as a multi-port VOA or a dynamic gain flattening device.